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CVE-2025-38429
bus: mhi: ep: Update read pointer only after buffer is written
Published 2025-07-25 (15 months ago) by the Linux kernel CNA. Subsystem drivers/bus. Debian urgency: not yet assigned.
Debian does not build this code. The per-release build detail is under "Where it lives" below.
What to do, per Debian release
Debian's own status for CVE-2025-38429 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| Debian 13trixie | fixed | 6.12.35-1 | Update the kernel and reboot. Fixed in 6.12.35-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 6.12.35-1 | Update the kernel and reboot. Fixed in 6.12.35-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 6.12.35-1 | Update the kernel and reboot. Fixed in 6.12.35-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Inside mhi_ep_ring_add_element, the read pointer (rd_offset) is updated before the buffer is written, potentially causing race conditions where the host sees an updated read pointer before the buffer is actually written. Updating rd_offset prematurely can lead to the host accessing an uninitialized or incomplete element, resulting in data corruption. Invoke the buffer write before updating rd_offset to ensure the element is fully written before signaling its availability.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
drivers/bus/mhi/ep/ring.c
- What this is
- MHI BUSMAINTAINERS section matched on drivers/bus/mhi/ · mhi@lists.linux.dev · Maintained
- Kernel module
- none to look for. The file would have gone into mhi_ep, and Debian does not compile it into that module, so finding mhi_ep in lsmod would say nothing about this CVE.
Check it on the machine
grep -w CONFIG_MHI_BUS_EP /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian does not build this code. In 4 releases below, every kernel flavour Debian publishes has the switch off, so the vulnerable file is compiled into no kernel binary Debian ships.
- bookworm, trixie, forky, sidn
- n
- not enabled on any flavour - this release does not build the code
- Build switch
- CONFIG_MHI_BUS_EP
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2025-07-25 (15 months ago)source
- CVSS
- 10.0 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.43%, higher than 36.2% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/bus
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.19 | 6.6.95 | 44b9620e82bb |
| 5.19 | 6.12.35 | f704a80d9fa2 |
| 5.19 | 6.15.4 | 0007ef098dab |
| 5.19 | 6.16 | 6f18d174b73d |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- MHI EP is the WWAN/modem datapath; event-ring insertions are generated per transfer completion for data crossing the link, including downlink packets originating from remote network peers, so a remote party driving traffic exercises the racy path with no local access to either side.
- AC:LAttack complexity, low
- The window between the MMIO rp publish and the eDMA element write is microseconds wide and the host polls rp continuously, so the race hits under ordinary traffic — the upstream host-side fix describes it as "the usual pattern" observed in practice, not a rare interleaving.
- PR:NPrivileges required, none
- No capability check, authentication step, or privilege gate exists anywhere along the path from traffic arrival to mhi_ep_ring_add_element(); event generation is driven purely by host doorbells and channel data movement.
- UI:NUser interaction, none
- The stale-element exposure occurs during normal automatic MHI event-ring operation; no victim action such as mounting, opening a device, or loading a module is required.
- S:CScope, changed
- The defect is in the endpoint's kernel MHI stack, but the resulting double free and DMA-unmap corruption occur in the host kernel on the other side of the PCIe link — a distinct processor and security authority, analogous to a device/DMA boundary crossing.
- C:HConfidentiality impact, high
- The host consumes an uninitialized or stale ring element and dereferences attacker-influenced TRE pointers, and the resulting use-after-free over already-completed buffers gives control of freed object contents suitable for arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- Upstream explicitly documents that this ordering bug causes the host to double-free transfer buffers and re-unmap DMA mappings, which is heap corruption exploitable for arbitrary write and control-flow hijack.
- A:HAvailability impact, high
- Double free, DMA unmap of already-unmapped buffers, and pending_pkts refcount underflow reliably oops or panic the host kernel and desynchronize the ring, tearing down the MHI link.